1. Technical Field
The invention relates generally to hockey sticks. More particularly, the invention relates to a hockey stick having a light-weight shaft which is highly durable, impact-damage-resistant and dynamically responsive. Specifically, the invention relates to a thin-walled hockey stick shaft made of titanium or a titanium alloy.
2. Background Information
Wood has been the traditional material of construction for ice and street hockey sticks. As such, the hard wood, Northern white-ash, is typically used in solid form for stick shafting (shafts) and blades. This hard wood has been attractive for hockey sticks based on high availability, flexibility, strength, hardness, ease of manufacturability into sticks, and, especially, low relative cost.
Produced from a natural product, however, wood sticks inherently exhibit strong property directionality (i.e. texture), a relatively low elastic modulus, weak areas from defects and/or grain and composition inconsistencies, significant variability in durability and stiffness, and property and dimensional changes and/or warpage over time (instability). Furthermore, wood is highly susceptible to mechanical damage (cracking, splitting, chipping, denting) when impacted, especially when damage is imposed parallel to the grain direction. Wood sticks can become brittle at either temperature extreme, and/or over time as the natural moisture content of the wood diminishes (i.e., dries out). Flexure characteristics can change over time with use. Wood also possesses inherent energy dampening qualities, which act to reduce elastic energy transfer (snap) from the stick to the puck being shot.
Some of these limitations with wood hockey sticks have been alleviated over the years through the application of fiberglass and/or carbon fiber reinforced plastic layers and laminates applied around the wood core. Not only does the fiberglass outer layer retard moisture egress from the wood core to extend stick shelf-life, it offers improved impact damage and cracking resistance to the wood. Furthermore, the glass and/or carbon fiber type and lay pattern can be used to enhance and control wood shaft and/or blade stiffness and dynamic response. Unfortunately, this fiberglass laminated and reinforced wood design results in fairly stiff and heavy hockey sticks (e.g., ˜660 grams for a one-piece stick).
In the pursuit to improve hockey stick durability, consistency, and achieve lower net weight, extruded hollow aluminum alloy shafts (thin-wall seamless rectangular tubulars) were introduced around the mid to late 1980's. With this design, a replaceable laminated wood blade is inserted (with hot glue) into the hosel end of the aluminum shaft. Aluminum alloys, such as the 7005 alloy typically used in tennis rackets and baseball bats, offered tempered yield strengths on the order of 45,000–50,000 pounds per square inch (psi), in combination with good flexibility (elastic modulus ˜10.1 million psi) and a low density of 0.10 lb/in3. In order to achieve the shaft stiffness and damage/impact tolerance required, these aluminum shafts were typically designed with 0.045–0.060″ thick constant or tapered walls. As a result, modest shaft weight reductions on the order of 10–15% were achieved over wood. This metal shaft also featured performance consistency, long-term stability, and damage tolerance/life extension, compared to wood sticks. The integration of composite materials with aluminum to create “hybrid” shafts in the early 1990's provided further means to trim shaft weight, enhance shaft dynamic response/energy transfer, and adjust/control stiffness. Here again, glass- and/or carbon-reinforced plastic laminates and/or Kevlar (aramid) wraps were applied over aluminum tubular core reinforcements to control stiffness and create flex points along the shaft length.
Despite these shaft material/design advances, commercial production of aluminum alloy hockey stick shafts has recently been discontinued. Fundamentally, this occurred due to the commercial availability of even lighter, more dynamically responsive, and often lower priced single-piece or two-piece all-composite sticks. Aluminum's inherent combination of lower strength and modulus properties limited the ability to design lighter weight sticks with the durability to withstand the rigors of hockey play. These aluminum shafts were known to suffer out-of-plane permanent set (yielding from bending), denting, and cracking in hosel corners.
With their market entry in the mid-1990's, all-composite shafts and one-piece sticks today represent approximately two-thirds of the hockey stick market in North America. Despite prices which can range from 3–6 times that of wood stocks, the current market predominance of all-composite hockey sticks/shafts primarily stems from three basic performance features:                1. Lower weight: Composite shafts typically weigh 280–340 grams, or roughly 460–500 grams for a one-piece hockey stick. This represents a net weight reduction in the range of 25–37% over wood. Lighter weight translates into a faster and/or harder shot.        2. A wider range of stiffness: Typically, offense players prefer less-stiff (more flexible) shaft response for puck control and wrist-shots with quick snap. Stiffer sticks are generally favored by defensemen for slap-shots. Shaft stiffness is often commercially rated on the unofficial scale of 70–120 lb/in, related to the load to achieve a shaft mid-span deflection of one inch.        3. Improved, consistent energy transfer: Composite shafts/sticks exhibit enhanced elastic energy storage and transfer to the puck compared to wood shafts. This stems from reduced matrix dampening and the nature of glass- and/or carbon-fiber lay. Unlike wood, these flex and energy characteristics are highly controlled and consistent from stick to stick.        
Despite these attractive performance features, inadequate durability and impact damage tolerance of these fiber-reinforced plastic composites represent their greatest limitations. Composites are well known for their minimal resistance to impact damage which can produce undetectable, internal mechanical damage to the composite (e.g., fiber-matrix separation). This internal damage is very sensitive to the degree and direction of impact, and the shape-hardness of the impacting body. Although composite shafts may utilize Kevlar outer sheet wraps to mitigate impact damage to the composite substrate, brittle, cracking failure of composite shafts is still life limiting. This lack of durability is very serious since each all-composite shaft currently typically retails for $70–100, and the one-piece composite stick is typically priced in the range of $170–200. This poor stick life cycle cost scenario has recently financially impacted professional hockey teams, where replacement composite stick budgets have skyrocketed. Less critical durability issues with composites include effects at extreme temperature limits. Repeated overheating of the shaft hosel area incurred during blade replacement procedure using hot glue can produce composite blistering and weakening, whereas very cold outdoor winter temperatures can make sticks more prone to brittle fracture.
U.S. Pat. No. 5,863,268 granted to Birch discloses a metal goalkeeper's hockey stick, which has a blade and shaft which are preferably formed of an aluminum alloy, but which may also be formed of a titanium alloy. However, the Birch hockey stick is specifically one used by a goalie or goaltender, which is completely different than that of a “player” hockey stick, that is, one used by the players (forward and defense men) other than the goalie. Goalie sticks and player sticks are not interchangeable with one another and indeed each would be completely inadequate if used in the stead of the other.
The goalie hockey stick is configured for a completely different purpose than the player hockey stick. The goalie stick is configured primarily for blocking shots or deflecting shots away and thus utilizes a substantially enlarged blade for that purpose, along with a substantially shortened shaft. By contrast, the player sticks are alternately used for maneuvering and/or passing the puck quickly while sometimes skating at high speeds; making wrist-shots with quick snap; and making slap-shots which launch the puck at high speed. Thus, sticks with various stiffness and flex characteristics are important in player sticks. Typically, forward or offensive players prefer less-stiff (more flexible) shaft response for puck control and wrist-shots with quick snap. Stiffer sticks are generally favored by defense men for slap-shots.
In keeping with the difference in purposes of the sticks, the blade of the goalie stick, as shown by Birch, has a horizontal portion and an upstanding portion which is substantially longer than (nearly twice as long as) the horizontal portion. In addition, the upstanding portion of the blade is roughly the same width as the horizontal portion. By contrast, the blade of the player stick has a relatively short upwardly extending portion, mainly for the purpose of providing a transition for connecting to the shaft. This upwardly extending portion is also substantially narrower than the horizontal portion of the player blade.
While the Birch shaft is a hollow tube, it is substantially shorter at approximately 32 inches than the shaft of the typical player hockey stick, which is roughly 50 inches, although this varies. Due in part to the relatively long upstanding portion of the goalie blade, a longer shaft is not suitable for use with the goalie stick. The substantially longer shaft of the player stick alone creates a completely different dynamic aspect from that of a goalie stick shaft. As a result of the distinct purpose and the correspondingly different size, the player stick shaft must incorporate various parameters quite distinct from those of the goalie stick shaft.